Method and device for the prevention of wall adherences in shafts on the introduction of particles

ABSTRACT

The invention relates to a process for inhibiting agglutination in a upright duct when particles are introduced, where at least some parts of the walls of the upright duct are wetted with a film of liquid, and also to an apparatus for carrying out the process, embracing an anterior panel ( 10 ), at least part of which is composed of a porous sheet and which has been arranged in front of at least part of the walls of the upright duct ( 2   a,    2   b ) and which forms with these a chamber ( 11 ) which can be filled with a liquid, where the apparatus also embraces a feed ( 9 ), and/or to tubes ( 5 ) which can be inserted, freely suspended, into an upright duct and can be filled with a liquid, and which have been arranged along the walls of the upright duct ( 2   a,    2   b ) and have a feed ( 6 ) and have discharge openings ( 7 ).

[0001] The invention relates to a process for inhibiting agglutinationin an upright duct when particles are introduced, and to an apparatusfor carrying out the process.

[0002] When impact-modified polystyrene or styrene copolymers areprepared, a rubber solution in styrene is introduced into thepolymerization plants. Rubber bales are comminuted to allow dissolutionof the rubber. The rubber is comminuted by being pressed through aperforated plate, followed by die-face cutting, using a rotating knife.The rubber particles pass via an upright duct into the dissolution tankwith styrene (A. Echte, Rubber-toughened styrene polymers, A Review, ACSSymposium Series 222, American Chemical Society: Washington, D.C., 1989,p. 15).

[0003] The rotating motion of the knife means that many of the rubberparticles are not projected vertically through the upright duct into thedissolution tank but thrown against the upright duct wall, to which theyadhere to a degree which depends on the tackiness of the rubber. Inextreme cases, these accumulations can completely block the path throughthe upright duct. One consequence of this is shutdown of the comminutionunit, and associated disruption of the entire polymerization plant.

[0004] A preventive measure used to avoid this is cleaning of theupright duct walls at regular intervals. This cleaning work consumestime and manpower. The work has to be carried out using respiratoryprotection if there is any likelihood of monomer emissions.

[0005] The use of conventional auxiliaries, such as pulverulent Znstearate or mineral oil, added during the comminution process, has beenproposed in order to reduce the tackiness of the rubber. Since thesubstances used have to be those which do not impair the properties ofthe impact-modified polystyrene product to be prepared, there is a widevariety of auxiliaries which cannot be added for technical reasons orfor reasons of cost or can be added only in limited amounts. Especiallywhen the type of rubber used is highly adhesive or the upright duct islong, the amounts of powder or mineral oil needed are very large.

[0006] It has also been proposed that the upright duct walls can begiven an antiadhesive coating. A disadvantage here, however, is thatboth layers of this type can very easily be removed by scraping and canbe damaged during cleaning by mechanical means.

[0007] Another possibility would be to use a spray jet to detach theagglutinated material. The spray mist can produce an atmosphere whichhas a greatly increased concentration of solvents or of monomers andwhich can require additional preventive safety measures. Experience hasshown that the nozzle openings rapidly block and impair theeffectiveness of the nozzles. Cleaning of the nozzles is not possible,since there is no access to the upright duct during the productionprocess. In addition, the nozzles project into the upright duct and canbe broken off or damaged, and can cause sparking, during any cleaningprocedure which uses mechanical aids. If the nozzles are installed fromoutside, holes would have to be made through the upright duct wall.

[0008] It is an object of the present invention to develop a low-cost,flexible and reliable process for inhibiting agglutination on the wallsof upright ducts when particles, in particular rubber particles, areintroduced, and to develop an apparatus for carrying out the processwhich does not have the abovementioned disadvantages. The apparatusshould in particular be capable of rapid and simple incorporation intoexisting plants without sacrificing productivity and without complicatedmodifications, it should also be capable of being removed again, ifdesired.

[0009] We have found that this object is achieved by means of a processfor inhibiting agglutination in an upright duct when particles areintroduced, where the walls of the upright duct are wetted with a filmof liquid.

[0010] The film of liquid may be formed by directing a liquidtangentially to the walls of the upright duct via tubes which havelongitudinal slits at the lower end.

[0011] In another embodiment of the invention, at least portions of thewalls of the upright duct may be designed as a porous sheet and may bewetted with a film of liquid.

[0012] One example of a suitable porous sheet is a sintered metal sheet.This permits the process of wetting with a film of liquid to be carriedout without jets or sprays.

[0013] Another way of forming a film of liquid is by directing a liquidtangentially to the walls of the upright duct via tubes which havelongitudinal slits.

[0014] The particles may be produced via a comminution apparatus andintroduced into the upright duct.

[0015] The process is particularly suitable for tacky particles, inparticular for rubber particles, such as polybutadiene rubbers orpolyacrylate rubbers. The liquid preferred in this instance for the filmof liquid is a dispersing agent or solvent appropriate for the rubber,preferably styrene, aliphatic or cycloaliphatic hydrocarbons, e.g.cyclohexane, or aromatic hydrocarbons, such as benzene, toluene orethylbenzene, or mixtures of styrene with aliphatic or aromatichydrocarbons, in particular styrene/ethylbenzene mixtures.

[0016] It is particularly preferable for at least part of the solvent ordispersant to be charged together with the rubber particles via anupright duct into a dissolution tank, and for at least some parts of thewalls of the upright duct to be wetted with a film of liquid. In thisway, very large amounts of liquid can be used to prevent agglutinationin the upright duct without additional dilution of the rubber solution.For continuously operated dissolution vessels with level control, aproven method is to divide the total flow of solvent into from 1 to 50%by volume, preferably from 1 to 30% by volume, in particular from 5 to15% by volume, for the film of liquid in the wall of the upright duct,and from 99 to 50% by volume, preferably from 99 to 70% by volume, inparticular from 95 to 85% by volume, for direct introduction into thedissolution tank. When styrene is used as main solvent component, thestream of solvent is generally preheated to about 40-80° C.

[0017]FIG. 1 shows an apparatus suitable for carrying out the process ofthe invention and inserted into, and suspended in, an upright duct (2)with lid (1). The apparatus essentially consists of tubes (5) which canbe inserted, freely suspended, into an upright duct and can be filledwith a liquid and which have been 40 arranged along the walls of theupright duct (2 a, 2 b) and have a feed (6) and have discharge openings(7).

[0018]FIG. 2 shows an enlargement, with the lower ends of the tubes, andwith the discharge openings (7) and (8). The shape selected for thedischarge openings (7) is advantageously such that under the processconditions overlapping films of liquid form and entirely wet the wall ofthe upright duct below the discharge opening. The admission pressure setis such as to cause discharge from the discharge openings of the amountof liquid needed for the wetting process. An admission pressure of fromabout 2 to 3 bar for the liquid is generally sufficient.

[0019] The size selected for the outlet openings (7) is preferably suchas firstly to inhibit any blocking and secondly to inhibit any splashingof liquid.

[0020] The number and arrangement of the discharge openings (7), and thelength of the tubes (5) depend on the shape of the upright duct and onthe location of any severe agglutination. The design preferably has thedischarge openings (7) as longitudinal slits measuring about 2×40 mm tothe lower end of the tubes, the arrangement of the longitudinal slitsbeing such that the liquid is directed tangentially to the walls of theupright duct (2 a, 2 b). The tubes (5) may have additional dischargeopenings (8) directed toward the walls of the upright duct (2 a, 2 b).

[0021] The cross section of the tubes (5) may be as desired, andpreference is given to using tubes whose cross section is round,rectangular or equilateral polygonal, for example triangular, square orhexagonal. A square or rectangular cross section for the tubes here hasproven particularly advantageous for optimizing the cleaning process.

[0022] The number of the tubes and their arrangement along the walls ofthe upright duct depend essentially on the shape of the upright duct. Ifthe duct is of square or rectangular shape, the preferred arrangement ofthe tubes is in the four corners of the upright duct.

[0023] The feed (6), and also the feed (9), may advantageously bedesigned as a supporting and distributing rack via which the tubes (5)and, respectively, the chamber (11) are supplied with liquid. Thesupporting and distributing rack may simply be installed between the endof the upright duct and the lid.

[0024] The discharge openings (7) of the tubes (5) are generallyarranged below an apparatus for feeding particles, for example onedesigned as a perforated plate (3) with a rotating knife (4).

[0025]FIG. 3 shows an apparatus suitable for carrying out the process ofthe invention, which is inserted, freely suspended, into an upright duct(2) and which comprises a lid (1). The apparatus essentially consists ofan anterior panel (10), at least part of which is composed of a poroussheet and which has been arranged in front of at least part of the wallsof the upright duct (2 a, 2 b) and which forms with these a chamber (11)which can be filled with a liquid, where the apparatus also embraces afeed (9).

[0026] This embodiment is particularly advisable when adapting anexisting plant. In order to avoid excessive narrowing of the opening ofthe upright duct, the thickness of the chamber (11) which can be filledwith liquid is generally selected in the range from about 0.5 to 2 cm.

[0027] However, it is also possible for some or all of the walls of theupright duct to be designed as a porous sheet.

[0028] The apparatus of the invention may additionally comprise tubes(5) which can be inserted, freely suspended, into an upright duct andcan be filled with a liquid and which have been arranged along the wallsof the upright duct (2 a, 2 b) and have a feed (6) and have dischargeopenings (7).

[0029] The tubes (5) may, for example, serve simultaneously as frame forthe anterior panel (10), at least part of which is composed of a poroussheet. The porous sheet is preferably installed in the region of thefeed apparatus.

[0030] The film of liquid is effective in the process of the inventionin inhibiting the agglutination of rubber particles which arrive at thewall of the upright duct as a result of the rotation of the wiper knife.

[0031] Another great advantage of the apparatus of the invention is thatit can be assembled and dismantled simply and rapidly at any timewithout shutting down the plant and without having to roll or cut holesin the upright duct, or place inserts into the same. Existing assembliescan be adapted without complicated extension or modification, andwithout any significant shutdown time, permitting the processing of evenhigh-tack varieties of rubber.

[0032] The apparatus permits the film of liquid to be directedspecifically at locations with severe agglutination, and is evensuitable for upright ducts of elongate shape.

EXAMPLE 1

[0033] An apparatus as in FIG. 1 was installed into a duct, about 1,900mm in length, of a rubber dissolution apparatus with a clear crosssection of 600×300 mm. The tubes (5) were produced from 20×20 mm squaretubes with wall thickness of 2 mm and length of 900 mm, and fittedprecisely into the four corners of the upright duct. The frontaldischarge openings (7) were designed as slits of length 15 mm, and theirshape permits non-splash discharge of the liquid and wetting of a majorarea of the wall of the upright duct. The openings (8) facing toward thewall of the upright duct were constructed as holes with a diameter of 3mm. The location of all of the discharge openings is at a depth of 850mm measured from the upper edge of the upright duct.

[0034] A substream of about 1,000 liters with a temperature of from40-80° C. was removed from the feed of the dissolution tank and passed,at a flow pressure of about 1.5 bar, by way of the four tubes (5) to thewalls of the vertical duct.

[0035] Wetting of the entire surface of the wall permitted longlastingavoidance of any adhesion of the comminuted rubber particles withresultant blocking of the vertical duct below the rotating knife.

EXAMPLE 2

[0036] An apparatus as in FIG. 3 was installed in an upright duct oflength about 1,900 mm with a clear cross section of 600×300 mm. The twoface sides (2 b) were completely covered by paneling at a distance of 20mm from the wall of the upright duct. The paneling of the upper 250 mmwas constructed as a pressure chamber on both sides. The chamber walltoward the interior of the upright duct was formed by sintered metalsheets (10). The porosity of the sintered metal sheets is 31% and theirthickness is 10 mm.

[0037] During operation, the pressure chamber was charged with oil, theinlet pressure being 1.5 bar. The amount of oil discharged from thesintered metal sheets which form the chamber wall is about 10 l/h perchamber, and this forms a coherent film of liquid across the sinteredmetal sheets, and also on the paneling-covered wall of the upright ductbelow the sintered metal sheets.

[0038] Even when using rubbers which have a marked tendency towardadhesion, the previous requirement for regular cleaning of the wall ofthe upright duct was entirely eliminated by this apparatus.

EXAMPLE 3

[0039] An arrangement which has proven particularly advantageouscomprises both the apparatus described in Example 1 and that describedin Example 2.

We claim:
 1. A process for inhibiting agglutination in a upright ductwhen rubber particles are introduced, which comprises wetting the wallsof the upright duct with a film of liquid, where the liquid usedcomprises a dispersing agent or solvent appropriate for the rubber.
 2. Aprocess as claimed in claim 1, wherein the film of liquid is formed bydirecting a liquid tangentially to the walls of the upright duct viatubes which have longitudinal slits at the lower end.
 3. A process asclaimed in claim 1, which comprises designing at least some parts of thewalls of the upright duct as a porous sheet and wetting these with afilm of liquid.
 4. A process as claimed in claim 3, wherein a sinteredmetal sheet is used as porous sheet.
 5. A process as claimed in claim 3or 4, wherein a film of liquid is also formed by directing a liquidtangentially to the walls of the upright duct via tubes which havelongitudinal slits.
 6. A process as claimed in any of claims 1 to 5,wherein the particles are produced via a comminution apparatus and thusintroduced into the upright duct.
 7. A process as claimed in any ofclaims 1 to 6, wherein the liquid used comprises styrene, aliphatic,cycloaliphatic or aromatic hydrocarbons, or a mixture of styrene withaliphatic, cycloaliphatic or aromatic hydrocarbons.
 8. A process forpreparing rubber solutions from rubber particles, which comprises addingat least some of the solvent together with the rubber particles via anupright duct into a dissolution tank, where at least some parts of thewalls of the upright duct have been wetted with a film of liquid.
 9. Anapparatus for processing rubber particles, encompassing tubes (5) whichcan be inserted, freely suspended, into an upright duct and can befilled with a liquid and which have been arranged along the walls of theupright duct (2 a, 2 b) and have a feed (6) and have discharge openings(7).
 10. An apparatus as claimed in claim 9, wherein the design has thedischarge openings (7) as longitudinal slits at the lower end of thetubes, the arrangement of the longitudinal slits being such that theliquid is directed tangentially to the walls of the upright duct (2 a, 2b).
 11. An apparatus as claimed in claim 9 or 10, wherein the tubes (5)have additional discharge openings (8) directed toward the walls of theupright duct (2 a, 2 b).
 12. An apparatus for processing rubberparticles, encompassing an anterior panel (10), at least part of whichis composed of a porous sheet and which has been arranged in front of atleast part of the walls of the upright duct (2 a, 2 b) and which formswith these a chamber (11) which can be filled with a liquid, and also afeed (9).
 13. An apparatus as claimed in claim 12, also encompassingtubes (5) which can be inserted, freely suspended, into a upright ductand can be filled with a liquid and have been arranged along the wallsof the upright duct (2 a, 2 b) and have a feed (6) and have dischargeopenings (7) designed as longitudinal slits, where the arrangement ofthe longitudinal slits is such that the liquid is directed tangentiallytoward the walls of the upright duct (2 a, 2 b).
 14. An apparatus asclaimed in any of claims 9 to 11 and 13, wherein four tubes (5) with around or polygonal cross section have been arranged in the corners of asquare or rectangular upright duct (2).
 15. An apparatus as claimed inany of claims 9 to 14, wherein the feed (9) and/or (6) has been designedas a supporting and distributing rack.
 16. An apparatus as claimed inany of claims 9, 10, 11, 13, 14 or 15, wherein the discharge openings(7) of the tubes (5) have been arranged below an apparatus for feedingparticles, designed as a perforated plate (3) with a rotating knife (4).17. An apparatus for the dissolution of rubber, which embraces arubber-comminution unit which has been arranged in an upright duct (2)installed above a dissolution tank, and has an apparatus for feedingparticles, designed as a perforated plate (3) with a rotating knife (4),wherein the upright duct (2) comprises a freely suspendable apparatus asclaimed in any of claims 10 to 16.